In recent years there has been an increasing emphasis on the use of lightweight composite materials. One application, for example, has been their use to improve the efficiency of motor vehicles. To that end, the United States Government and the U.S. Council for Automotive Research (USCAR)—which represents Daimler Chrysler, Ford, and General Motors have partnered to form the Partnership for a New Generation of Vehicles (PNGV). One goal of PNGV is to develop technology, such as composite technology, that can be used to create environmentally friendly vehicles with up to triple the fuel efficiency, while providing today's affordability, performance and safety. For example, PNGV wants to improve the fuel efficiency of today's vehicles from about 28 miles per gallon (mpg) to about 83 mpg and a 40-60% decrease in the present curb weight (3200 pounds).
One method to improve the fuel efficiency is to decrease the weight of today's vehicles and use lighter weight materials. The materials used in today's vehicles, such as steel and aluminum, are quite heavy relative to composite materials, but have been necessary to provide sufficient structural properties, including tensile, compression, flexural, interlaminar shear, and in-plane shear strengths and other mechanical and material properties, to meet vehicle design requirements.
Many other applications of lightweight composites have been made to supplement or replace the use of structural materials, such as steel, cast iron, and aluminum. These include buildings, bridges, recreational vehicles, aerospace, defense, and sporting goods, as well as many other applications.
Composites are a mixture or combination, on a macro scale, of two or more materials that are solid in the finished state, are mutually insoluble, and differ in chemical nature. Types of composites include laminar, particle, fiber, flake, and filled composites. Composites, however, often have not had the combination of structural properties mentioned above and/or low cost necessary to promote their wide-spread use in motor vehicle and other applications.
Despite their lack of structural strength, some composite materials have been employed in vehicle manufacturing. For example, laminated composite tubes above have been used as structural members in vehicles to reduce the weight and increase the energy absorbing characteristics. Typically, the tube is generally straight over its length and resists axial impacts at the end of the tube by absorbing the energy of the axial impact and crushing at that location. Known means for energy absorption by crushing in composite tubes, include knife-edges, slits, bevels and plugs, and the like at the end of the tube as described in U.S. Pat. Nos. 4,742,899, 5,732,801, and 5,914,163, the disclosures of which are incorporated herein by reference. The crushing characteristics, however, of such composite materials are still fairly limited when compared to more traditional structural materials. For example, such energy absorption means do not exhibit the desired progressive crush beginning at any selected location other than the end of the tube.
One way to increase the structural properties of composite materials, particularly the torsional or flexural strength, is to make them in a more structurally efficient form. In one more structurally efficient form, composite materials have been combined with a supporting structure, such as a honeycomb or foam structure, by sandwiching the supporting structure between panels of the composite material. Examples of such combinations have been described in U.S. Pat. Nos. 5,006,391, 5,195,779, 5,652,039, 5,834,082, 5,848,767, 5,849,122, and 5,875,609, the disclosures of which are incorporated herein by reference. Such combinations, however, have been generally limited to relatively flat structures and so the use of such materials have been quite limited.